Storing it and transferring it on the server is one thing; serializing it locally in the browser itself might be a more reasonable goal? That is, it wouldn't be expected to be portable to anything but that very same browser, but it would allow you to cache the compiled result. (I would expect the serialized string to be signed by the browser itself, to prove that it was created by the browser – and for the deserialization to fail on some browser upgrades).
Care would have to be taken to ensure that these blobs cannot be mutated via other means, or that a non-function blob can be converted to a function blob with passing through validation, otherwise it might be an attack vector, for someone to figure out the internal representation, and manipulate storage to forge one that trips up some fast-path code which makes assumptions about the input being correct.
Right, that's the idea of FunctionBlob. It wraps a browser-internal representation of the optimized compiled code. The web code can instruct the browser to store that offline, without exposing its implementation-specific details to the web code. The web code can then, in a later session, retrieve that optimized code from storage as another FunctionBlob, which it can then convert into a Function. This is no different from just storing the asm.js source code in offline storage, except it avoids redoing the work of compiling and optimizing the source. (It'd still have to be stored in position-independent format and there might be some back-patching necessary when reloading it.)
